箭頭功能意外輸出

Question

我有以下箭頭功能。

var a = 10;
var b = 5;
var str = (a,b) => ("sum: "+(a+b));

str();

我期望輸出是

sum: 15

但輸出是

sum: NaN

為什么？

Answer 1

var a = 10;

var b = 5;

var str = (a, b) => ("sum: " + (a + b));

str(a, b); // You have to call the function with parameters. 

Answer 2

您必須傳遞參數str(a,b) 。

var a = 10;
var b = 5;
var str = (a,b) => ("sum: "+(a+b));

str(a,b);

Answer 3

您沒有在調用函數時傳遞參數a和b

 var a = 10; var b = 5; var str = (a, b) => ("sum: " + (a + b)); console.log(str(a, b));